Joss Whedon left social media a while ago, but he's returned for a good cause. He's using Twitter to promote a new project that's "focused on getting people to register to vote." Whedon created a PSA video for savetheday.vote and he enlisted some of his celebrity friends like Robert Downey Jr., Scarlet Johansson, Don Cheadle, Mark Ruffalo and more to help get out the message. In a statement from Save the Day, the organization says it's "dedicated to the idea that voting is a necessary and heroic act."